Where did you see the key board shortcut for inset page break?? I can't find it in the help menu nor does the Insert menu show that there is a keyboard shortcut. This is what the Pages User Guide says:
+Here are ways to insert a page break:+
+In a word processing document, click where you want the break to occur, and then+
+choose Insert > Page Break.+
+To remove a page break, click at the beginning of the line that follows the break and+
+press the Delete key.+
+In a page layout document, to insert a new page in your document, click Pages in the+
+toolbar and choose from the template page options available.+
BUT I found that you can use Shift + numeric Enter. On my MBP I use Shift + fn-key + enter
That is how one did it in AppleWorks and it seems to work in Pages too!